1. Field of the Invention
The present invention relates to a CT scanner including a plurality of sets of X-ray tubes and X-ray detectors.
2. Description of the Related Art
In a CT scanner of a rotate/rotate (R-R) system, a set of an X-ray tube and an X-ray detector are arranged to face each other on a rotary stand. Moreover, in this CT scanner, the X-ray tube and the X-ray detector obtain projection data while rotating around a subject, and an image in the subject is reconstructed from the projection data.
In diagnosis of an internal organ such as the heart which moves quickly, scanning needs to be completed in a short time in order to obtain a clear image. It is effective to increase a rotation speed of the stand in order to realize such scanning in the R-R system. However, when the rotation speed of the stand is raised, a centrifugal force rises in proportion to a square of the rotation speed. Therefore, in general, 0.3 second/rotation degree is a limitation.
Consequently, a technology is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-52640 in which a plurality of sets of X-ray tubes and X-ray detectors are mounted, and these simultaneously collect the projection data, so that a scanning time is reduced without raising the rotation speed.
However, when high-voltage devices are mounted on the plurality of X-ray tubes, a weight of the stand increases, and this lengthens the time required from a time when the rotation of the stand is started until the rotation is stabilized. Since a plurality of X-ray high-voltage devices are simultaneously operated, power supplied to a rotary portion of the stand increases, and the life of a slip ring shortens. Since output voltages of the X-ray high-voltage devices fluctuate, a difference is made in tube voltages of the plurality of X-ray tubes, and an artifact might be generated.
Furthermore, since the plurality of X-ray tubes simultaneously emit X-rays from different directions, an image blurs under influences of scattered rays.